Dual fuel engines are known for various applications, such as generator sets, engine-driven compressors, engine driven pumps, machine, off-highway trucks, marine applications and others. Typically, such engines are stationary and operate in the field. The operation of such engines by substitution of a certain amount of heavy fuel, such as diesel, with a lighter fuel, such as natural gas, biogas, liquid petroleum gas (LPG) or other types of fuel that may be more readily available and cost effective, makes them more effective to operate.
Nevertheless, it is often the case that the quality of the secondary fuel available in certain areas is not consistent. For example, when the secondary fuel is biogas generated onsite at an area, or even LPG or natural gas purchased from local sources, the fuel heating value and/or the methane number of these fuels is certain to vary over time or for different batches of fuel purchased. Such changes in the methane number or fuel heating value require various changes to the operation of the engine, such as diesel fuel injection amounts, injection timing, and the like, so that efficient engine is maintained.
Moreover, in typical dual fuel engine such as an engine operating to burn natural gas, the burning of which is initiated by a diesel pilot, significant time is spent in a laboratory to map out acceptable gas substitution rates across the operating range of the engine, while maintaining acceptable cylinder pressure, exhaust temperature and other engine operating parameters within hardware limits. Given the inherent variability in natural gas composition, these calibration techniques are often conservative and can lead to possible losses in relative to engine performance that can be achieved theoretically. All these and other factors add cost and complexity to the operation of an engine in the field.